The present invention relates to a photopolymerizable composition for use in making, for instance, paints, printing inks and printing materials such as letterpress and lithographic printing materials.
There have been known a variety of polymerization initiators for monomers which have a radical-polymerizable ethylenically unsaturated bond capable of generating a radical through the irradiation with Uv rays and in particular, benzophenones, Michler's ketones, fluorenones, xanthones, thioxanthones or the like have been well known.
However, if these compounds are used in the photopolymerizable compositions as photopolymerization initiators, they are not sufficiently sensitive to light rays from a light source which shows a strong emission spectra at the long wavelength range such as a metal halide lamp because of the structures of these compounds In addition, in a system to which a pigment such as titanium oxide is added, the absorption spectra of the pigment are superimposed with those of the photopolymerization initiator. Therefore, the quantity of light rays having a desired wavelength required for the photopolymerization initiator to cause a desired polymerization is reduced and hence only insufficient sensitivity of the initiator can be attained.
Verious methods have been proposed for solving the foregoing problem. For instance, Japanese Patent Unexamined Publication (hereinafter referred to as "J.P. KOKAI") No. Sho 61-145203 discloses that a certain kind of halogen-substituted acridone compound has an improved high sensitivity to the foregoing light rays of long wavelengths. These compounds can certainly show high sensitivity, but it is still insufficient from the practical viewpoint and thus there has been desired for the development of a photopolymerization initiator having higher sensitivity.